I have the MX Keys Mini keyboard. I turn the backlight at the end of the day and use it for about 1 hour, sometimes 2 hrs. But the next morning, I forget to turn it off, and it stays on for several days, even though I do not need backlight during the day, depleting battery life. 
I would love to be able to turn backlight for 6 hours: when using the keyboard FN key F5 to increase the backlight, it increase backlight in this order:- no backlight- level 1 for 12 hours- level 1- level 2 for 12 hours- level 2- level 3 for 12 hours- level 3- level 4 for 12 hours- level 4- level 5 for 12 hours- level 5- level 6 for 12 hours- level 6- level 7 for 12 hours- level 7
That way, say I turn it on at 6 pm on Monday, when its dark already during winter in Switzerland, and work until 9 pm. That means I would use backlight for 3 hours on Monday night, and by Tuesday morning, backlight would be turned off again. And then, if I only work past 6 pm on Friday again, backlight is off during the entire week, and on Friday I use FN+F5 to turn it on at my desired intensity for another 12 hours. I would not be surprised that many customers that change backlight, do it to conserve battery life, and they would welcome this feature.